1. Field of the Invention
The invention relates to a method of measuring venous pressure.
The invention also relates to an arrangement for measuring venous pressure.
The heart pumps and causes blood to flow in the blood vessels, arteries and veins. The pumping produces pressure in the blood, i.e. blood pressure. Blood pressure is particularly affected by heartbeat and the resistance provided by peripheral circulation. Psychic factors, medication, smoking and other factors, such as a person""s state, i.e. whether a person is asleep or awake, are also important.
2. Brief Description of the Related Art
The terms systolic pressure, diastolic pressure and venous pressure, are used when discussing blood pressure. Technically, from the point of view of measurement, systolic pressure refers to the pressure at which an artery becomes blocked, i.e. heartbeat stops. Physiologically, systolic pressure refers to the maximum pressure generated by a pumping cycle of the heart.
Technically, from the point of view of measurement, diastolic pressure refers to the pressure at which heartbeat is resumed when the pressure pressing the artery is reduced. Physiologically, diastolic pressure refers to the minimum arterial pressure value between two pumping cycles of the heart.
Venous pressure refers to the average pressure in a vein. At a certain stage of venous pressure measurement, a systolic and diastolic point can also be detected. Technically, from the point of view of measurement, venous pressure refers to such acting compressive pressure which, when acting, causes a vein to be occluded by the acting pressure. Occluded veins cause an increase in the tonus of the arm, i.e. an increase in the swelling of the arm, since once the arteries are occluded, blood remains in the arm as it has no way of returning. A typical value of venous pressure, measured from the arm, is between 20 and 30 mm Hg. The magnitude of venous pressure is indicative of the loading status of the heart, fluid balance and the condition of the circulation and blood vessels of the person who is the subject of the measurement.
Up to now, venous pressure has been measured invasively, i.e. intravenously from an artery. The drawback in the invasive method is naturally that the measurement is made from inside a person""s body by the use of e.g. a catheter placed in a vein. The invasive method and the equipment solutions involved are unpleasant for a person, and the measurements involve much work and are cumbersome, since they require operating theater conditions. A special drawback is the risk of infection and bleeding of the artery. It has been known to use non-invasive methods, such as the auscultatory method, oscillometric method and manual palpation method for measuring diastolic and systolic pressure. The difficulty of the present venous pressure measurement method restricts the usability of measuring venous pressure in diagnostics. Venous pressure is measured mainly when the load of the atrium is observed during the filling state.
It is an object of the present invention to provide a new kind of method and arrangement for measuring venous pressure, avoiding the problems of known solutions.
This object is achieved by a method of the invention, characterized in that the measurement is made non-invasively by applying a variable compressive acting pressure to a measuring point, such as a person""s extremity or the like, at a compression point by a pressure generator, and at the same time the effect of the variable acting pressure on the circulation is measured at a second point, the second point being located farther away from the heart, i.e. closer to the end point of peripheral circulation, than the compression point to which the acting pressure is applied, and that the measured value of the variable pressure acting on the measuring point at the compression point is transferred to an interpreting unit to which is also applied a pressure pulse caused by the heart and measured at said second point by a sensor to measure the effect of the variable acting pressure, and that in the interpreting unit venous pressure is determined on the basis of an acting pressure which is measured by a measuring element and which is the acting pressure when the interpreting unit detects a change characteristic of venous pressure in the pressure pulse signal measured by said sensor.
The measurement arrangement of the invention is characterized by comprising a pressure generator for applying a compressive acting pressure to a measuring point, such as a person""s extremity or the like, at a compression point, the arrangement comprising a measuring element for non-invasive measurement of the acting pressure, and the arrangement further comprising an interpreting means for determining venous pressure, and the arrangement comprising a sensor for simultaneously non-invasively measuring the effect of the variable acting pressure on the circulation at a second point, said second point being located farther away from the heart, i.e. closer to the end point of peripheral circulation, than the compression point to which the acting pressure is applied, and said sensor which measures the effect of the variable acting pressure being a sensor which measures the pressure pulse generated by heartbeat and which is coupled to said interpreting unit to which is also coupled a measured signal indicating the measured value of the acting pressure, and the interpreting unit being arranged to determine the venous pressure non-invasively on the basis of an acting pressure which is the pressure acting when the interpreting unit detects a change characteristic of venous pressure in a pressure pulse signal measured by the sensor which measures the artery.
The method and measurement arrangement of the invention are based on the idea of using a sensor which measures arterial pressure pulse and transfers its measurement data to the interpreting unit to indicate from the measured acting pressure signal the point corresponding to venous pressure.
The solution of the invention provides a plurality of advantages. The invention provides an extremely good measurement accuracy, allowing the value of venous pressure to be determined extremely accurately, since its detection is based on a separate measurement of the pressure pulse, which is used to indicate the value of venous pressure. The result of the pressure pulse measurement depends on the change in the tonus of the measuring point, i.e. swelling, since as the tonus rises, the skin contact of the pressure pulse measuring sensor improves, whereby a rise in the measured amplitude of the pressure pulse is observed.